Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$43.41	12.565%	$48.8645	$48.86	$48.85	$48.90
Purchase #2	$205.27	4.536%	$214.581	$214.58	$214.60	$214.60
Purchase #3	$148.85	7.664%	$160.2579	$160.26	$160.25	$160.30
Purchase #4	$84.51	5.329%	$89.0135	$89.01	$89.00	$89.00
Purchase #5	$71.59	4.849%	$75.0614	$75.06	$75.05	$75.10
Purchase #6	$184.89	11.135%	$205.4775	$205.48	$205.50	$205.50
Purchase #7	$36.38	11.724%	$40.6452	$40.65	$40.65	$40.60
7 purchase totals =	$774.90		$833.9010	$833.90	$833.90	$834.00